Abstract
Laser Terahertz Emission Microscopy (LTEM) is a method which has been developed in order to study intrinsic carrier dynamics in semiconductors with a spatial resolution which is only limited by the wavelength of the incident fs laser [1]. More recently, it has been shown that the spatial resolution in a terahertz (THz) spectroscopy experiment can be improved even further by utilizing plasmonic coupling of the incident THz field to a subwavelength metal tip, which has resulted in resolutions on the order of 10 nm [2]. As previously proposed [3] we here present our first results on LTEM with nanometer resolution by combining the two methods mentioned above as illustrated in Fig. 1 (a) where the incident fs laser pulses (100 fs, 800 nm, 80 MHz) are coupled to a sharp metal tip with a spatial diameter of sub-20 nm. The THz pulses emerging from the sample are detected by EO sampling in a 2 mm thick ZnTe crystal with lockin detection to the tapping frequency of the AFM probe (20 kHz). The tapping amplitude of the AFM probe is approximately 40 nm and the length of the probe is 80 µm ± 20% (Rocky Mountain Nanotechnology). In addition, we demonstrate how the detected LTEM signal can be modulated by applying a bias on the AFM probe while keeping the sample on a ground plane.
© 2017 IEEE
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